1. Technical Field
The invention concerns optical memories including the type of optical memory embodied in a compact disk and compact disk drive.
2. Background Art
The most popular form of an optical memory is the compact disk with a compact disk drive used with personal computers, for example, and compact disk player used with high-fidelity stereo sound systems. The compact disk is an aluminum platter having pits stamped in the surface, each pit corresponding to one bit of information, or each pair of neighboring pits representing a differentially encoded bit. The top and bottom surfaces of the aluminum platter are covered with a hard plastic coating. Manufacturing the disk merely involves stamping the aluminum platter with a desired pit pattern and then coating the platter. The optical disk drive or disk player has a spindle on which the disk is mounted for rotation, a laser, an optical detector and a lens which scans the laser's beam radially across the disk surface while the disk rotates. The signal produced at the detector can be processed to deduce the sequence of pits in the disk.
The capacity of such a memory is limited by the number of pits that can be recorded in the disk. This in turn is limited by the disk diameter and the minimum spot size which the optics in the player or disk drive is capable of resolving. Generally, the bit capacity of the memory corresponds to the maximum number of bits recordable on the disk.